A male bibionid fly, smaller than the one in my earlier post, and with reddish-brown legs. Probably either Bibio johannis or Bibio lanigerus (Diptera: Bibionidae), but my photo is really too blurry for me to tell. [Note added 2011-04-01: According to this comment by Theo Zeegers at Diptera.info, the hairs on the bodies of B.johannis males are black, while the hairs on B. lanigerus males are white, so the above male must be B. lanigerus.]
And this is a female of the same species (the female's eyes are much smaller than the male's). These two flies were on the same bush and flew round each other, touching several times.
Photos taken in the Wilderness, Whiteknights Park, Reading University grounds, Reading, UK, on 2010-04-13.